linux-kernel - Re: [PATCH] x86: Remove unnecessary kmap() from sgx_ioc_enclave

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Date:   Tue, 2 Feb 2021 19:37:08 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Sean Christopherson <seanjc@...gle.com>, ira.weiny@...el.com,
        linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org
Subject: Re: [PATCH] x86: Remove unnecessary kmap() from
 sgx_ioc_enclave_init()

On Mon, Feb 01, 2021 at 08:48:12AM +0000, Christoph Hellwig wrote:
> On Fri, Jan 29, 2021 at 09:37:30AM -0800, Sean Christopherson wrote:
> > On Thu, Jan 28, 2021, ira.weiny@...el.com wrote:
> > > From: Ira Weiny <ira.weiny@...el.com>
> > > 
> > > There is no reason to alloc a page and kmap it to store this temporary
> > > data from the user. 
> > 
> > Actually, there is, it's just poorly documented.  The sigstruct needs to be
> > page aligned, and the token needs to be 512-byte aligned.  kmcalloc doesn't
> > guarantee alignment.  IIRC things will work until slub_debug is enabled, at
> > which point the natural alignment behavior goes out the window.
> 
> Well, there still is absolutely no need for the kmap as you can use
> page_address for a GFP_KERNEL allocation.

Yeah, we do that in sgx_ioc_enclave_create already based on feedback:

        secs = kmalloc(PAGE_SIZE, GFP_KERNEL);
        if (!secs)
                return -ENOMEM;
        
The kmap() in sgx_ioc_enclave_init() is an unfortunate miss. Let's just
follow the pre-existing pattern.

/Jarkko